Being known as a metallic material having superior mechanical strength and chemical durability, titanium has long been used in various fields. For instance, titanium-based electrodes are exclusively used in modern electrolytic equipment for producing chlorine and sodium hydroxide by electrolysis of aqueous sodium chloride. The titanium-based electrodes comprise a titanium substrate coated with an electrode active material and, in order to ensure higher electrode performance as manifested by prolonged service life and lower overpotential, the substrate desirably has an adequately large surface area and strong adhesion to the coating. To this end, it has been proposed to roughen the surface of the titanium substrate by either blasting or etching but the increase in surface area can be achieved only with respect to a shallow surface layer and the anchor effect attained is not strong enough to provide firm adhesion to the coating material.
Porous titanium materials which are generally spongy or fibrous are known (see, for example, Japanese Patent Application (OPI) No. 8416/80 (the term "OPI" means an unexamined published application)) but they are not suitable for use in applications where high mechanical strength is required.
There are many metallic members that require high physical and chemical strength, large surface areas and a high capacity for anchoring the coating material: they include, in addition to the electrode substrate described above, carrier supports for use in chemical reactors and metallic materials for biocompatible implants such as artificial bones. However, no titanium-based materials have been developed to date that satisfy all of the requirements for use in these applications.